1. Field of the Invention
This invention relates to an improved process for the hydrogenation of maleic acid, maleic anhydride or other hydrogenatable precursor to 1,4-butanediol and tetrahydrofuran. The process is characterized by the use of a catalyst comprising palladium, silver and rhenium on a carbon support. The process is also characterized by high yields of 1,4-butanediol with minimal formation of by-product gamma-butyrolactone.
2. Description of the Prior Art
It is well known that tetrahydrofuran, gamma-butyrolactone and 1,4-butanediol are obtained by the catalytic hydrogenation of maleic anhydride and related compounds. Tetrahydrofuran is a useful solvent for natural and synthetic resins and is a valuable intermediate in the manufacture of a number of chemicals and plastics. Gamma-butyrolactone is an intermediate for the synthesis of butyric acid compounds, polyvinylpyrrolidone and methionine. Gamma-butyrolactone is a useful solvent for acrylate and styrene polymers and also a useful ingredient of paint removers and textile assistants. 1,4-butanediol (a.k.a. 1,4-butylene glycol) is useful as a solvent, a humectant, an intermediate for plasticizers and pharmaceuticals, a cross-linking agent for polyurethane elastomers, a precursor in the manufacture of tetrahydrofuran, and is used to make terephthalate plastics.
Of particular interest in the instant invention are hydrogenation catalysts comprising palladium, silver and rhenium on a carbon support, which are useful for the hydrogenation of maleic anhydride, maleic acid and related compounds to tetrahydrofuran, gamma-butyrolactone and 1,4-butanediol.
British Patent No. 1,534,232 teaches the hydrogenation of carboxylic acids, lactones or anhydrides using a hydrogenation catalyst consisting of palladium and rhenium on a carbon support. U.S. Pat. Nos. 4,550,185 and 4,609,636 teach a process of making tetrahydrofuran and 1,4-butanediol by hydrogenating maleic acid, maleic anhydride or other hydrogenatable precursor in the presence of a catalyst comprising palladium and rhenium on a carbon support wherein the palladium and rhenium were present in the form of crystallites having an average palladium crystallite size of about 10 to 25 nm and an average rhenium crystallite size of less than 2.5 nm. The preparation of this catalyst is characterized by the deposition and reduction of the palladium species on the carbon support followed by the deposition and reduction of the rhenium species on the palladium impregnated carbon support.
U.S. Pat. No. 4,985,572 teaches a process for the catalytic hydrogenation of a carboxylic acid or an anhydride thereof to the corresponding alcohol and/or carboxylic acid ester using a catalyst comprising rhenium, palladium and silver on a carbon support. The preparation of this catalyst is characterized by the simultaneous deposition of palladium and silver on the carbon support followed by a high temperature (600.degree. C.) heat treatment. Rhenium was then deposited on the palladium/silver impregnated carbon support. The resulting catalyst was then reduced.
Generally, in the hydrogenation of maleic acid, maleic anhydride or other hydrogenatable precursor the above discussed catalyst has the propensity to produce more tetrahydrofuran and gamma-butyrolactone than 1,4-butanediol. An object of this invention is a process and a catalyst which will maximize 1,4-butanediol production and minimize gamma-butyrolactone production.